The present invention relates to disc recorders and, more specifically, to recorders in which video information is recorded on a flexible magnetic disc. The magnetic disc used typically may be a laminate construction in which a cloth material is sandwiched between two layers of thin flexible material. The layers of flexible material are coated with magnetic particles and define the recording surfaces of the disc. The recording disc is rapidly rotated and one or more transducer heads are positioned in contact with the disc to record and reproduce the video information. If desired, transducers may be provided for recording and playback on both sides of the magnetic disc.
Recording of video signals on a disc recorder may be accomplished with one of several formats. In one format, the video signal is stored in a number of circular concentric recording tracks and the transducer is moved only intermittently to the desired track for recording or playback. In a second format, the transducer head is moved continuously in a radial path as the disc is rotated, thus defining a continuous, spiral recording track.
The flexible magnetic disc used in such a recorder is rotated at a speed which is sufficiently high to generate centrifugal forces making it unnecessary to support the disc at a point other than its center. It can be appreciated, however, that tension of the disc, resulting from the outwardly directed centrifugal forces created during rotation, will be much less at a point near the periphery of the disc than at a point near its center. This is so because the mass of the material outward from a point near the periphery of the disc is much less. Since the transducer heads used in a flexible disc recorder actually make contact with the disc surface and exert a slight pressure on that surface, the recording surface of the disc will tend to be distorted more out of its plane of rotation by a transducer head when the transducer head is in contact with a point near its periphery than when the head is positioned radially inward. This non-uniformity in the distorting effect of the transducer head on the flexible recording surface results in non-uniform transducer effectiveness unless some provision for compensation is made.
A typical transducer head consists of two cores on which one or more groups of windings have been wound. Each core is separated from the other by non-magnetic material, thus defining a gap. When the windings on the cores are energized, the fringing flux at the gap will magnetize particles in the coating on the recording surface of the disc. During playback, the magnetized particles passing adjacent the gap will generate flux flow through the cores and induce current flow in the windings. For effective recording and playback it is necessary that the recording disc be maintained in a closely coupled relationship with the transducer head on both sides of the gap. Distortion of the recording surface of the flexible disc as the transducer head moves radially toward the periphery of the disc may prevent the transducer head from maintaining the desired positional relationship with respect to the disc. This may occur even when transducer heads are positioned exactly opposite each other on both sides of the disc, since the center cloth lamination tends to isolate the recording surfaces from each other.